Process for the preparation of unsaturated acids

ABSTRACT

ALPHA-BETA UNSATURATED OLEFINS, PARTICULARLY PROPYLENE, ARE OZIDIZED IN THE VAPOR PHASE BY MOLECULAR OXYGEN, WITH THE PRODUCTION OF THE CORRESPONDING UNSATURATED CARBOXYLIC ACIDS, PARTICULARLY ACRYLIC ACID.

United States Ratent O US. Cl. 260-533 N 2 Claims ABSTRACT OF THEDISCLOSURE Alpha-beta unsaturated olefins, particularly propylene, areoxidized in the vapor phase by molecular oxygen, with the production ofthe corresponding unsaturated carboxylic acids, particularly acrylicacid.

THE PRIOR ART The oxidation of olefins to the corresponding unsaturatedcarboxylic acids has been described in various patents according towhich the reaction occurred either in a single phase and led directly tothe desired product, or in two phases, the olefins being oxidlzed to thecorresponding unsaturated aldehyde in the first phase, and the aldehydebeing oxidized to the desired unsaturated carboxylic acid in the secondphase.

For the production of the unsaturated carboxyllc acids on an industrialscale, the single phase process is preferred. A great variety ofcatalysts may be used in that process.

However, it is known that, in general, the results obtained are notentirely satisfactory. One drawback is that, in addition to theunsaturated carboxylic acid, considerable quantities of unsaturatedaldehyde are formed and must be recycled in order to obtain asatisfactory yield of the acid. In an industrial operation, suchrecycling is a burdensome, uneconomical disadvantage.

THE PRESENT PROCESS The primary object of the present invention is toprovide a process for oxidizing the unsaturated alpha-beta olefins tothe corresponding unsaturated aliphatic carboxylic acids in good yieldsand with the formation of the aldehydes in such minimum quantities thatrecycling thereof is not necessary. More particularly, it is an objectof the invention to oxidize propylene to high yields of acrylic acid,with minimum formation of the intermediate aldehyde and hence theelimination of any need for recycling the latter.

These and other objects are accomplished by this invention in accordancewith which alpha-beta olefins are oxidized to the correspondingunsaturated aliphatic carboxylic acids by reacting the alpha-beta olefinand molecular oxygen in a vapor phase, at temperatures of from 300 C. to500 C., and in the presence of a catalyst consisting of molybdenum,vanadium, tellurium, oxygen and, in the given case, other elementscapable of combining with tellurium to form alloys or tellurides inwhich there is present at least one of oxygen, molybdenum, and/ orvanadium, and/or tellurium having an oxidation state lower than themaximum.

The ratios between the elements constituting the catalyst may varywithin a Wide range. Thus, for 1 gram atom of molybdenum there may beused from 2.0 to 0.05 gram atoms of vanadium and from 2.0 to 0.02 gramatoms of tellurium, preferably from 1.0 to 0.1 gram atom of vanadium andfrom 1.0 to 0.1 gram atom of tellurium. In order to obtain suchcatalysts, the molybdenum and vanadium are subjected, for example asammonium salts, to a heat treatment at temperatures comprised between350 C. and 550 C., in the absence of oxygen. The tellurium may be addedeither before or after the heat treatment.

In a preferred embodiment, the catalyst used in the present process isprepared by evaporating an aqueous solution of ammonium para-molybdateand ammonium meta-vanadate to dryness, and then subjecting the productthus obtained, to a heat treatment at temperatures comprised between 350C. and 550 C., for a time varying from 2 to 16 hours, and in the absenceof oxygen. Tellurium, tellurium dioxide, or a metal telluride, forinstance, nickel telluride, is then mixed mechanically with theheat-treated product.

In another preferred embodiment, the catalyst is prepared by evaporatingan aqueous solution of ammonium para-molybdate, ammonium meta-vanadate,and telluric acid to dryness and subjecting the product thus obtained toheat treatment at temperatures comprised between 350 C. and 550 C., forfrom 2 to 16 hours, in the absence of oxygen.

Instead of using the ammonium salts of molybdenum and vanadium asstarting materials for preparation of the catalyst, the oxides of thoseelements may be used, for instance molybdenum trioxide and vanadiumpentaoxide. In that case, the oxides are mixed together and the mixtureis then subjected to a heat treatment in the presence of a gascontaining ammonia, and at temperatures comprised between 350 C. and 550C.

Besides tellurium metal, other products containing the element may beused, such as, for instance, tellurium dioxide, metal tellun'des,telluric acid, and ammonium tellurate.

The catalyst may be used with or without a carrier. Suitable carriers orsupports include silica, alumina, silicaalumina, pumice stone, siliciumcarbide, etc. Furthermore, the catalyst may be used as a fixed or as afluidized bed.

The reaction temperature may vary from 300 C. to 500 C., but ispreferably in the range 350 C. to 420 C.

The reaction may be conducted at atmospheric pressure, or it may beconducted at increased pressure (e.g., up to 10 absolute atms.) in orderto increase production of unsaturated acid.

The contact time, defined as the ratio between the apparent volume ofthe catalyst and the volume of the fed gas under the given reactionconditions in a unit of time, may vary from 0.05 to 25 seconds, but ispreferably from 0.5 to 10 seconds.

The oxygen used to oxidize the alpha-beta olefins may originate from anyappropriate source. Air is preferred. The oxygen/olefin molar ratio maybe from 0.5:1 to 5:1, and is preferably from 1:1 to 3:1.

The oxidation is preferably conducted in the presence of one ormorediluents, such as: nitrogen, steam, carbon dioxide, and saturatedhydrocarbons. The yield in unsaturated acidsis quite independent fromthe nature of the diluents. It has now been found that the presence ofsteam increases the quantity of acetic acid produced. Therefore, if itis desired to limit the acetic acid production it is convenient to useother diluents, in particular nitrogen.

However, steam may be useful for its effectiveness in dissipating thereaction heat, or when the formation of acetic acid is not undesirable.Furthermore, steam permits an increase in the concentration ofpropylene, restricting the inflammability of the air/propylene mixture.

The present invention provides a very advantageous process for thepreparation of alpha-beta unsaturated aliphatic carboxylic acids,particularly acrylic acid. In fact,

about 120 Nl/hour of a gas consisting of 10% of ammonia and 90% ofnitrogen. At various time intervals, 40 g. samples were taken out and toeach sample there was added the same quantity (3.8 g.) of nickeltelluride (NiTe The samples were then kneaded, dried, granulated andfinally tested on the equipment specified in Example 1.

The following table shows the results of these tests carried out at atemperature of 370 C., under a pressure of 1.2 absolute atm., with acontact time of 2 seconds and with a feed-mixture consisting of 5% byvolume of propylene, 42.5% of air and 52.5% of nitrogen.

1 From the examination of the above table it can be seen how theduration of the reducing treatment shows an optimum.

Conversion of olefin in moles of fed olefin moles of unreacted olefinM0165 of fed olefin X 100 Selectivity of the products in g. atoms ofcarbon in the product X100 g. atoms of carbon in the reacted olefin Inall the examples the reaction products were determined by means of a gaschromatograph.

EXAMPLE 1 175.6 g. of ammonium paramolybdate were dissolved in 300 cc.of water. Thereupon there were added 22.8 g. of ammonium metavanadateand the whole was then heated until complete dissolution was attained.This solu tion was evaporated to dryness and the product was reducedinto granules and subdivided into three parts: a, b and c, which wereactivated at the same temperature of 450 C., for the same period of time(8 hours), but in difierent atmospheres, i.e.:

part a: in an air current; part b: in a nitrogen current, and part c: ina current of nitrogen containing 10% of NH 50 g. of each activatedproduct were admixed with 4.9 g. of tellurium dioxide, kneaded with alittle water, dried and reduced into granules having a diametercomprised between 0.2 and 0.3 mm., thereby originating respectivelycatalysts A, B and C.

The catalysts were tested by filling them into a steel reactor 100 mm.long and with an inside diameter of 10 mm., immersed in a bath of moltentin, into which was sent a gaseous mixture consisting of 5% by volume ofpropylene, 42.5 of air and 52.5% of nitrogen.

At a temperature of 400 C., under a pressure of 1.2 atm. and with acontact time of 0.7 second, the following results were obtained:

Selectivity (percent) in- Over a product based on molybdenum andvanadium, obtained as described in Example l-part a, were passed,through a Pyrex glass pipe, at a temperature of 450 C.,

From the examination of the above table it can be seen how the durationof the reducing treatment shows an optimum.

EXAMPLE 3 An aqueous solution containing 55 g. of ammoniumparamolybdate, 7.26 g. of ammonium meta-vanadate and 7.14 g. of telluricacid, was evaporated to dryness and subsequently subejected toactivation in a nitrogen current at 450 C., for 8 hours. Thereby, acatalyst was obtained which was used in an oxidation test carried out onthe same equipment cited in Example 1, using a feedmixture consisting of5% by volume of propylene, 42.5% of air and 52.5% of nitrogen, at atemperature of 360 C. and under a pressure of 1.2 absolute atm., with acontact time of 2 seconds.

The results thereby obtained were as follows:

Percent Conversion of propylene 84.6

Selectivity in acrylic acid 67.4

Selectivity in acrolein 3.0

Selectivity in acetic acid 4.8

Selectivity in Co +CO M8 EXAMPLE 4 Percent Conversion of propylene 90.0Selectivity in acrylic acid 66.4 Selectivity in acrolein 9.7 Selectivityin acetic acid 2.9 Selectivity in CO +CO 21.0

EXAMPLE 5 45 g. of a product based on molybdenum and vanadium, obtainedas described in Example 1 (part b), were soaked with an aqueous solutioncontaining 5.3 g. of telluric acid.

The product thus obtained was then dried in an oven and additioned withan aqueous solution containing hydrazine in excess for reducing thetelluric acid to metaltellurium. Thereupon, the product was againbrought to dryness and was then heated up to 300 C. in a nitrogencurrent in order to eliminate the excess hydrazine. Finally, the productwas granulated to particles having a diameter comprised between 0.2 and0.3 mm. It was then tested under the same reaction conditions as thoseused in Example 1, except for the temperature which was kept at 370 C.and the contact time which was maintained at 2 seconds. The results ofthese tests were the following:

Percent Conversion of propylene 85 Selectivity in acrylic acid 67Selectivity in acrolein 9 Selectivity in acetic acid 3 Selectivity in CO+CO 21 EXAMPLE 6 49 g. of a product based on molybdenum and vanadium,obtained as described in Example 1 (part b), were additioned with 5.0 g.of molybdenum and cobalt telluride (CoMoTe With this mixture a catalystwas prepared which was tested under the same conditions as thosespecified in Example 5. The results were as follows:

Percent Conversion of propylene 86 Selectivity in acrylic acid 67Selectivity in acrolein 7 Selectivity in acetic acid 3 Selectivity inCO-l-CO 23 EXAMPLE 7 40 g. of a product based on molybdenum andvan-adium, obtained as described in Example 1 (part b), were additionedwith 3.8 g. of nickel telluride. With this mixture a catalyst wasprepared and tested under the same conditions as those of Example 2. Theresults were as follows:

Percent Conversion of propylene 88 Selectivity in acrylic acid 65Selectivity in acrolein l2 Selectivity in acetic acid 3 Selectivity inCO +CO 20 EXAMPLE 8 Over the same catalyst as used in Example 7, Waspassed a gaseous mixture consisting of 5% by volume of propylene, 42.5%of air, 25% of steam and 27.5% of nitrogen.

Under the same reaction conditions as those used in Example 5, theresults obtained were as follows:

Percent Conversion of propylene 90 Selectivity in acrylic acid 61Selectivity in acrolein 4 Selectivity in acetic acid 12 Selectivity inCO +CO 23 EXAMPLE 9 The results of experiments carried out with a numberof catalysts in which the Te/Mo atomic ratio varied, while the V/ Moatomic ratio remained constant and equal to 0.2 are recorded on thetable that follows.

' To a compound based on molybdenum and vanadium, obtained as describedin Example 1 (part b), was added tellurium in the form of molybdenum andcobalt telluride (CoMoTe The recorded data refer to tests carried outwith a feed-mixture consisting of 5% by volume of propylene, 55% of air,40% nitrogen, at a temperature of 360 C., under a pressure of 1.2absolute atm. and with a contact time of 2 seconds. The test equipmentwas the same as that described in Example 1.

Catalyst Atomic ratio, Te/Mo Conversion, percent. Selectivity (percent)in:

Acrylic acid Acrolein Acetic acid. OOH-CO 8 EXAMPLE 10 Catalyst Atomicratio, V/Mo 0.05 0.10 0.20 0.50 1.00 2.00 Conversion, percent 56.0 75.589.0 92.5 89.4 88.2 Selectivity (percent) in: 39 4 EXAMPLE 1 1 g. ofammonium paramolybdate were dissolved in 400 cc. of water. To thissolution were then added 72.6 g. of ammonium meta-vanadate and themixture was evaporated to dryness under constant stirring. The dryproduct was then activated in a Pyrex tube in a nitrogen current at 450C. for 8 hours.

50 g. of the activated product were additioned with 33.3 of Nite thenmixed, kneaded with a little water, dried and finally reduced togranules having a diameter comprised between 0.2 and 0.3 mm.

Into a reactor like that described in Example 1, charged with the abovegranules, was fed a mixture consisting of 5% by volume of propylene, 55%of air and 40% of nitrogen. At a temperature of 360 C., under a pressureof 1.2 absolute atm., and with a contact time of 2 seconds, thefollowing results were obtained:

Percent Conversion of propylene 90.8 Selectivity in acrylic acid 58.7Selectivity in acrolein 4.7 Selectivity in acetic acid 4.9 Selectivityin CO +CO 31.7

EXAMPLE 12 36 g. of ammonium paramolybdate were dissolved in 350 cc. ofwater. To this solution were then added 48.5 g. of ammonium metavanadateand the mixture was evaporated to dryness under stirring.

The dry product was activated in a Pyrex glass tube in a nitrogencurrent, at 450 C. for 8 hours. 50 g. of the activated product wereadditioned with 48.2 g. of NiTe mixed, kneaded with a little water,dried and finally reduced into granules having a diameter comprisedbetween 0.2 and 0.3 mm. The tests with this catalyst, conducted asdescribed in Example 11, gave the following results:

Percent Conversion of propylene 93.7 Selectivity in acrylic acid 41.8Selectivity in acrolein 6.8 Selectivity in acetic acid 8.2

Selectivity in CO +CO 43.2

7 EXAMPLE 13 35.1 g. of ammonium paramolybdate were dissolved in 80 cc.of water. To this solution, there were added 4.6 g. ammoniummetavanadate and the whole was heated to obtain a solution in which 3.8g. of telluric acid were dissolved.

The solution was used to impregnate 81 g. of microspheroidal silica. Theproduct thus obtained was dried in an oven at 110 C. and then activatedfor 8 hours in a current of nitrogen at 450 C. The carrier represented70% by weight of the whole catalyst.

By passing over said catalyst a gaseous mixture consisting of by volumeof propylene, 37.5% of air and 57.5% of nitrogen, at a temperature of370 C. and under a pressure of 1.2 absolute atm. and with a contact timeof 4 seconds, the following results were obtained:

Percent Conversion of propylene 65 Selectivity in acrylic acid 52Selectivity in acrolein 4 Selectivity in acetic acid 12 Selectivity inCO -I-CO 32 The same feed-mixture was sent onto the same catalystfluidized in a reactor having an inside diameter of 70 mm. (380 cc. ofcatalyst). Under the same conditions as those indicated above, theresults were as follows:

Percent Conversion of propylene 57.0

Selectivity in acrylic acid 45.9

Selectivity in acrolein 3.4

Selectivity in acetic acid 7.4

Selectivity in CO +CO 43.3

EXAMPLE 14 47.4 g. of ammonium paramolybdate were dissolved in H O. Tothis solution were then added 3.1 g. of ammonium metavanadate and themixture was heated until a solution was obtained, which was then broughtup to a volume of 76 cc. This solution was used to impregnate 69.6 g. ofmicrospheroidal silica. The product thus obtained was dried in an ovenat 110 C., then activated in an N current at 420 C., for 8 hours; it wasagain impregnated with an aqueous solution containing 5.16 g. oftelluric acid, and finally was dried again at 110 C.

By sending over said catalyst a gaseous mixture consisting of 5% byvolume of propylene, 55% of air and 40% of nitrogen, at a temperature of400 C., under a pressure of 1.2 atm., and with a contact time of 1second,

the following results were obtained:

. Percent Conversion of propylene 82 Selectivity in acrylic acid 55.6Selectivity in acrolein 1.8 Selectivity in acetic acid 9.0 Selectivityin CO +CO 33.6

EXAMPLE 15 A gaseous mixture consisting of 8.4% by volume of propylene,67.6% of air, and 24% of steam was fed over a catalyst exactly like thatdescribed in Example 4.

At a temperature of 405 C., under a pressure of 1.2 absolute atm., andwith a contact time of 1.5 seconds, the following results were obtained:

Percent Conversion of propylene 91.8

Selectivity in acrylic acid 65.4

Selectivity in acrolein 4.3

Selectivity in acetic acid 8.0

Selectivity in C'O -l-CO 22.3

EXAMPLE 16 305 g. of a product based on molybdenum and vanadium,prepared and activated as described in Example 1 (part b), were mixedwith 147.5 g. of nickel telluride.

With this mixture was then prepared a catalyst in granules having adiameter comprised between 1.7 and 2.8 mm.

About 222 cc. of the granules were introduced into a tubular steelreactor having an internal diameter of 20 mm. and which was immersed ina heating bath of molten salts. Into this reactor were then fed 146Nl/hr. of a gaseous mixture consisting of 5% by volume of propylene, 55of air and 40% of steam. The inside temperature of the reactor wasmaintained at 373 C. Thereby, the following results were obtained:

Percent Conversion of propylene 83.6

Selectivit in acrylic acid 66.5

Selectivity in acrolein 6.2

Selectivity in acetic acid 8.5

Selectivity in CO -I-CO 18.8

EXAMPLE 17 A test was carried out on a catalyst prepared as described inExample 7, but activated at a temperature of 420 C., using afeed-mixture consisting of 5% by volume of propylene, 55% of air and 40%of nitrogen, at a temperature of 350 C., under a pressure of 1.2absolute atm., and with a contact time of 3 seconds.

The testing technique was that described in Example 1. During the test,a high percentage of air was used in order to determine whether, withtime, the phenomenon of reoxidation of the catalyst with the consequentloss of the starting performance level would occur. However, the resultsrecorded in the following table show how the activity of the catalystremained constant with time.

Conversion, Selectivity (percent) inpercent Progressive of AcrylicAcetic time, hours Oil-I5 acid Acrolem acid OOH-CO EXAMPLE 18 35.0 g. ofammonium paramolybdate were dissolved in water. To this solution werethen added 4.7 g. of ammonium metavauadate and the mixture was heated toobtain a solution which was then brought up to a volume of 98 cc. withwater.

The final solution was used to impregnate 89.7 g. of microspheroidalsilica. The product thus obtained was dried in an oven at C., activatedin a nitrogen current for 8 hours at 450 C., impregnated again with anaqueous solution containing 22.9 g. of telluric acid and, finally, driedagain at 110 C.

By sending over this catalyst a gaseous mixture consisting of 5% byvolume of propylene, 55% of air and 40% of steam at a temperature of 380C., under a pressure of 1.2 absolute atm., and with a contact time of 2seconds, the following results were obtained:

Percent Conversion of propylene 87.3 Selectivity in acrylic acid 69.8Selectivity in acrolein 4.1 Selectivity in acetic acid 3.5 Selectivityin CO +CO 22.6

As will be apparent, various changes in details can be made inpracticing this invention, without departing from the spirit thereof.Therefore, it is intended to include in the scope of the appended claimsall modifications which will be obvious to those skilled in the art fromthe description and examples given herein.

We claim:

1. A process for preparing acrylic acid, characterized in that propyleneand molecular oxygen are reacted in vapor phase at a temperature of from300 C. to 500"v C. and in contact with a catalyst consisting ofmolybdenum, vanadium, tellurium and oxygen and obtained from molybdenumand vanadium ammonium salts which have been heat-treated in advance, inthe absence of oxygen, in a nitrogen gas atmosphere, and at atemperature of from 350 C. to 550 C., and from a tellurium compoundselected from the group consisting of tellurium dioxide, telluric acidand nickel telluride and cobalt-molybdenum telluride, thevanadium/molybdenum atomic ratio in the catalyst being 0.05 to 2.0, andthe tellurium/molybdenum atomic ratio therein being from 0.02 to 2.0.

2. The process according to claim 1, in which the heattreatment iscarried out in a gaseous 10% ammonianitrogen mixture.

References Cited UNITED STATES PATENTS 3,192,259 6/1965 Fetterly et al.260-533 N 3,240,806 3/1966 Bethell et a1 260-533 N 3,435,069 3/1969Bethell et a1 260-533 N 3,439,028 4/1969 Yanagita et a1. 260-533 NX3,457,303 7/1969 Eden 260-533 N FOREIGN PATENTS 971,666 9/1964 UnitedKingdom 260-533 N 1,086,523 10/1967 United Kingdom 260-533 N HENRY R.JILES, Primary Examiner R. D. KELLY, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF. CORRECTION Pate t USP 3.736, 355 Dated Ma L29. 1933 Inventor) Mauro Croci and Enrico CavaterraIt is certified that error appears in the aboveidentified patent andthat said Letters Patent are hereby corrected as shown below:

Col. l, item 5, under the heading Acrolein" the numeral "3. 6" iscorrected to 3. 5-

Col. 6, in the 5th column of the Table under Example 10, the fourthnumeral "4. 3" is corrected to 4. 2- I Q Col. 8, in the third column ofthe Table under Example 17, the 6th numeral "57. 8" under the heading"Acrylic acid" is corrected to Signed and sealed this 9th day of Aprill97h.

' (SEAL) Attest:

EDI/JARD MELETCHERJR. C. MARSHALL DAT-IN Attesting Officer ICommissioner of Patents DRM PO-1 O50 (IO-69) USCOMM-DC BOS76-F'69 itUvS. GOVERNMENT PRINTING OFFICE I959 0-366-334.

